public sealed class Singleton3
{
    private Singleton3()
    {}

    private static object syncObj = new object();

    private static Singleton3 instance = NULL;
    public static Singleton3 Instance
    {
        //get
        if (instance == null)
        {
            lock(syncObj)
            {
                if(instance == null)
                    instance = new Singleton3();
            }
        }
        return instance;
    }
};